In cellular communications networks, wireless terminals, sometimes referred to as UEs (User Equipment), communicate wirelessly with base stations of the cellular communications network. In the downlink, from the base station to the UE, the UE may receive signals in a single frequency band associated with a single radio-frequency (RF) carrier. In order to improve the capacity (e.g. in terms of downlink bitrate), the concept of carrier aggregation (CA) has been introduced in 3GPP (3rd Generation Partnership Program) standards. Using CA, the UE may simultaneously receive a plurality of RF carriers. These RF carriers are normally referred to as component carriers, or CCs. On each CC there is modulated an information signal, e.g. an OFDMA (Orthogonal Frequency Division Multiple Access) signal or a CDMA (Code-Division Multiple Access) signal, carrying payload data and/or control information. The CCs may be located within the same operating frequency band, in which case the CA is referred to as intra-band CA. Alternatively, the CCs may be located within different operating frequency bands, in which case the CA is referred to as inter-band CA. For intra-band CA, the plurality of CCs may be located contiguously (in frequency), in which case the CA is referred to as contiguous CA, or may be non-contiguously located (in frequency) with frequency gaps in between, in which case the CA is referred to as non-contiguous CA. In one scenario, the UE may be allocated a primary CC (PCC) associated with a primary cell (PCell) of the cellular communications network. When an increase in downlink capacity is needed, for whatever reason, the UE may additionally be allocated one or more secondary CCs (SCCs) associated with respective secondary cells (SCells).
One solution for enabling the UE to receive a plurality of CCs, particularly in a non-contiguous CA scenario, is to use a receiver circuit with a plurality of receive paths, each connected to the same antenna, e.g. via a common low-noise amplifier (LNA). Each receive path may be responsible for reception of a particular one of the plurality of CCs. For example, each receive path may be of direct-conversion type, comprising a mixer unit driven by an LO signal having a frequency selected such that the mixer unit directly down-converts the particular CC to base band. The LO-signal frequency of each processing path may thus be selected in dependence of the RF frequency of the CC it is set to receive.